This is fairly subtle. The fact that the numbers are printed with a decimal point hints that they are floating point numbers. Floating-point arithmetic's inexactness makes equality tests less valuable than for, e.g., Integer arithmetic. If you change the "**"s to "^"s you'll get [3,4], etc. (or [3,4,5] if you change "[x,y]" to "[x,y,z]"). mike gunter E.g.: Main> [[x,y,z] | x<-[1..50],y<-[1..50],z<-[1..50],x^2+y^2==z^2] [[3,4,5],[4,3,5],[5,12,13],[6,8,10],[7,24,25], ... ]

Hello! I am reading Discrete Mathematics Using a computer by Hall and O'Donnell and in the introduction to hugs section, they give this example: [[x,y] | x<-[1..50],y<-[1..50],z<-[1..50],x**2+y**2==z**2] now I type it in and expect it to return a number of results, but it doesn't, it shows: [[8.0,15.0,17.0],[14.0,48.0,50.0],[15.0,8.0,17.0],[15.0,20.0,25.0],[20.0,15.0,25.0],[21.0,28.0,35.0],[27.0,36.0,45.0],[28.0,21.0,35.0],[30.0,40.0,50.0],[36.0,27.0,45.0],[40.0,30.0,50.0],[48.0,14.0,50.0]] My question is where is [3.0,4.0,5.0],[5.0,12.0,13.0]? I have looked everywhere I could think of to see what I am doing wrong, but I have no idea. Maybe a rounding error somewhere? Thank you, Scott Anderson